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Description of problem: When I do test on s390x machine, the console printed following messages: -------------------------------- ibm-z10-25 login: 01: HCPGSP2627I The virtual machine is placed in CP mode due to a SIGP initial C PU reset from CPU 00. cpu: Processor 1 started, address 0, identification 32C5C2 01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP stop from CPU 01. cpu: Processor 1 stopped ------------------------- the same console output when I do "echo 1 > /sys/devices/system/cpu/cpu1/online" Version-Release number of selected component (if applicable): 2.6.32-118 How reproducible: always Steps to Reproduce: 1. install RHEL6.1-20110224.2 on s390x machine 2. run some test, eg, /kernel/power-management/gettimeofday 3. Actual results: above console output is printed, and cpu1 can not be up. Expected results: Additional info: installed an older kernel 2.6.32-94, the same result.
With RHEL6.0, a program called "cpuplugd" manages the available CPUs depending on the work load of the system. The cpuplug daemon is enabled by default. Whenever a CPUs is switched online/offline, you can see a message with ID "HCPGSP2629I". This is an information message from the z/VM control program (CP). If the system is idle, the cpuplugd switches off additional CPUs, for example, to reduce z/CM CP scheduling efforts. It also allows to run with a certain overcommitment. Regarding your issue, if you manually switch an CPU online, cpuplugd will turn it offline on the next check interval. For your tests, you can stop cpuplugd with "/etc/init.d/cpuplugd stop", or you can use chkconfig to switch off cpuplugd permanently.